A piezo-electric speaker 40 of the prior art has, as shown in FIG. 10, has a completely round piezo-electric member 41 generating a vibration according to an electric signal applied thereto. A piezo-electric vibration plate 42 is adhered to the piezo-electric member 41 to convert the vibration to a sound. The piezo-electric member 41 and the piezo-electric vibration plate are adhered to each other with the centers of them being aligned.
However in the piezo-electric speaker 40 of the prior art, since the piezo-electric vibration plate 42 is made of a metallic plate-shaped member with less stretchability, no-vibrating portions are caused on the piezo-electric vibration plate 42 by a distortion such as creases generated during vibration. This makes it difficult to ensure a uniform sound in a broad band.
Since the diameter of the piezo-electric vibration plate 42 is limited, a large distortion of the piezo-electric vibration plate is caused when a signal of large sound is applied and therefore it is difficult to reproduce a clear sound. In addition, since the number of resonance point is limited, the sound pressure would be remarkably increased or reduced at particular frequencies corresponding to resonance points.